KABUL -- A former Afghan official says pressure is mounting on Pakistan to end its support for extremist groups who were reportedly involved in last week's assassination of former Afghan President Burhanuddin Rabbani, RFE/RL's Radio Free Afghanistan reports.

Ali Ahmad Jalali, an Afghan-American professor at the United States National Defense University in Washington, told RFE/RL on September 23 that recent comments by Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, have added to the pressure on Pakistan's intelligence agency, the Inter-Services Intelligence (ISI), to sever ties with extremist groups such as the Haqqani network.

"The U.S. has issued its strongest statement yet to Pakistan's ISI on its ties with the Taliban and Haqqani groups," said Jalali, who served as Afghan defense and interior minister from 2003-2005. "It is a clear message to Pakistan that it can no longer continue its current strategy in Afghanistan."

Mullen on September 22 accused the ISI of aiding the Haqqani network in planning and executing last week's attacks on the U.S. Embassy in Kabul. He said the Pakistani government had used the Haqqani network and other terrorist groups as its proxies in Afghanistan.

Mullen said Pakistan had chosen to "use violent extremism as an instrument of policy," adding that "by exporting violence, they have eroded their internal security and their position in the region. They have undermined their international credibility and threatened their economic well-being."

Jalali said "Pakistan has to come to terms [with the fact] that it cannot get what it wants in Afghanistan through violence and hard power. It must open up to diplomatic channels and use avenues such as the current peace council to state its concerns and ideas."

Jalali thinks that after the killing of Rabbani, Afghanistan must unite as a nation and learn from the experience.

"Until the people in Afghanistan unite in a common cause, its enemies will use these divisions to their advantage and promote their own agendas," he said. "We [Afghans] must come together."